1. Field of the Invention
The present invention relates to a device of a camera for detecting the direction in which the user is looking and, more particularly, a visual line direction detecting device which can be applied to a camera designed to perform automatic focus/exposure control by using detected visual line direction information.
2. Description of the Related Art
Information such as distance measurement or photometric information is input to a conventional camera by operating a dial, a button, or the like. In general, however, as the amount of information to be input is increased, an input operation tends to be complicated. For this reason, a method has been proposed, in which the visual line direction of a user of a camera who is looking into the finder is detected, and instructions are given to the camera on the basis of the visual line direction information.
For example, in the technique associated with the automatic focus adjustment camera disclosed in Published Unexamined Japanese Patent Application No. 61-61135, even if a major object to be photographed, on which the camera is to be actually focused, is net located in the center of the finder, focus adjustment can be performed In accordance with the distance to the major object by detecting the visual line of the operator who is looking into the finder and automatically directing a detecting section to the major object to which the visual line of the operator is directed. According to this technique, therefore, focus adjustment with respect to a major object, on which the camera is to be actually focused, can be easily performed.
In the technique associated with the camera control device disclosed in Published Unexamined Japanese Patent Application No. 63-94232, the visual line direction of a user inside a finder is detected so that instructions from the user can be judged on the basis of the position information.
In addition, according to the technique associated with the automatic focusing (AF) device disclosed in Published Unexamined Japanese Patent Application No. 1-190177, a visual line direction inside the finder visual field frame of a camera is detected, and a predetermined range almost coinciding with the visual line direction is displayed on the finder visual field frame, thereby detecting the focal point of an object to be photographed inside the field of vision.
Furthermore, in Published unexamined Japanese Patent Application Nos. 1-241511 and 2-5, techniques of detecting the above-mentioned visual line direction are disclosed.
Moreover, according to the technique associated with the visual line direction detecting device for a camera, disclosed in, e.g., Published Unexamined Japanese Patent Application No. 2-5, the light-receiving section of the device is constituted by a one-dimensional line sensor, and the processing circuit includes a splitting means for splitting an output from the one-dimensional line sensor into a fundus reflected light output component corresponding to reflected light from the fundus, and an output component corresponding to reflected light forming a first Purkinje image. The processing circuit obtains the position of the center of gravity of the split fundus reflected light component and that of the output component corresponding to the reflected light forming the first Purkinje image, respectively, thereby detecting the visual line direction of the eye.
In the above-described conventional techniques, when an optical system for performing visual line direction detection is to applied to a camera, the visual line direction detecting optical system is arranged in a split optical path in a finder optical system.
FIG. 14 shows the basic arrangement of a conventional visual line direction detecting device for performing visual line direction detection in a single-lens reflex camera.
As shown in FIG. 14, a quick return mirror 11 is disposed on the optical path of light passing through a photographic lens 10. A screen 12 and a finder liquid crystal display (LCD) 13 are arranged on the optical path of the light reflected by the quick return mirror 11. A pentaprism 14 is disposed on the optical path of the light passing through the screen 12 and the finder LCD 13. In addition, a prism 15 and an eyepiece 16 also serving as optical members for visual line direction detection are arranged on the optical path of the light reflected by the reflecting surface of the pentaprism 14.
A sub-mirror 80 is disposed on the optical path of the light transmitted through the quick return mirror 11. An AF sensor 81 is disposed on the optical path of the light reflected by the sub-mirror 80. An infrared light-emitting diode (LED) 21 and a light-emitting lens 22 are arranged as an illuminating section for visual line direction detection. Furthermore, a light-receiving sensor 31 and a light-receiving lens 32 are arranged as a light-receiving means for visual line direction detection.
Referring to FIG. 14, reference numerals 82 and 83 respectively denote a shutter and a portion (film rail surface) of the camera main body. A conventional camera generally has the above-described arrangement.
In this arrangement, light passing through the lens 10 is reflected by the quick return mirror 11. The reflected light is incident on the screen 12 and the finder LCD 13. The contents displayed by the LCD 13 can be superposed on an object to be photographed on the screen 12, The light passing through the screen 12 and the finder LCD 13 is reflected by the reflecting surface of the pentaprism 14. The reflected light is incident on the prism 15 and the eyepiece 16.
Meanwhile, the light transmitted through the quick return mirror 11 is reflected by the sub-mirror 80. The reflected light is then input to the AF sensor 81.
In this case, in order to perform visual line direction detection, an initialization input operation is generally performed to store the position of a reflected image on the light-receiving sensor 31, formed when the user looks into a predetermined intra-finder display, and the visual line direction of the user is detected on the basis of the movement amount of the reflected image from the set position. Although not necessarily required, this operation is preferably performed because the optical characteristics of the eyeball vary from person to person, and the optical characteristics of the right and left eyes of each person differ from each other.
In the above-described conventional techniques, however, since the finder optical system and the visual line direction detecting optical system partly share the same components, the following problems are posed.
Some conventional cameras incorporate diopter adjustment mechanisms, each designed to move the eye-piece as part of the finder optical system in accordance with the diopter of the user, and some are designed to adjust the diopters of the cameras by inserting lenses with diopters into the eyepiece portion of the cameras. Of the cameras incorporating zoom lenses and having non-transistor transistor logic (TTL) finders, some cameras are designed to perform zooming operations of the finder optical systems upon interlocking with zooming operations of the photographic lenses. In the above-described cameras, if diopter adjustment is performed after the above-mentioned initialization input operation is performed, the optical relationship between the visual line direction detecting optical system and the user greatly varies, even though the optical relationship between the finder optical system and the user is adjusted. In addition, the same problems as described above is posed when the magnification of the finder optical system is changed.
FIGS. 15A and 15B show a change in the state of the above-described visual line direction detecting optical system.
More specifically, FIG. 15A shows a state in which the eyepiece 16 is at the initial position, e.g., the position corresponding to -1 diopter, and light from the LED 21 is radiated, as a beam of parallel rays, on an eyeball 90. In the state shown in FIG. 15A, the illuminating and light-receiving optical systems for visual line direction detection are arranged such that the light reflected by the eyeball 90 is focused on the light-receiving sensor 31. When the eyeball 90 rotates to change the visual line direction, the detection image on the light-receiving sensor 31 moves, and the visual line direction of the user is calculated by a visual line direction calculating section 5.
FIG. 15B shows a state in which the eyepiece 16 moves to a position corresponding to the diopter of the user, and light from the LED 21 is radiated, as divergent light, on the eyeball 90.
In the state shown in FIG. 15B, the focal length and magnification of the illuminating and light-receiving optical systems for visual line direction detection change from those set while the eyepiece 16 is at the initial position.
In this state, light reflected by the eyeball 90 is not focused on the light-receiving surface of the light-receiving sensor 31. In addition the movement amount of the reflected image differs from the state shown in FIG. 15A upon rotation of the eyeball 90 and a consequent change in the visual line direction.
FIG. 16 is a graph showing the relationship between the rotational angle of the eyeball 90 and the movement amount of the image on the light-receiving sensor 31. Referring to FIG. 16, characteristics represented by lines 90a and 90b correspond to FIGS. 15A and 15B, respectively. As shown in FIG. 16, the movement amount of the image on the light-receiving element differs with a change in the magnification of the visual line direction detecting optical system. As a result, a correct visual line direction detection result cannot be output. This is because, the amount and direction of change in magnification differ depending on a finder and a visual line direction detecting system employed. That is, since the light-emitting/light-receiving optical systems of the visual line direction detecting optical system are not maintained in a constant state, the state of the visual line direction detecting optical system changes every time the focal point or magnification of the finder optical system is changed. Consequently, visual line direction detection cannot be performed.